1. Field of the Invention
The present invention relates generally to devices and methods for monitoring of analytes that may be found in body fluids, and more particularly to an apparatus and method for continuous noninvasive monitoring and measurement of analytes found in vascular and extravascular body fluid pools including interstitial, lymph and cerebral spinal fluids.
2. General Background and State of the Art
It is desirable to have a method for measuring or monitoring the levels of analytes present in the body fluids in a noninvasive manner. By noninvasive is meant a manner that does not require breaking the skin of the subject to obtain a measurement. Breaking the skin, or otherwise invading the body of the subject, can require a skilled medical technician to perform the procedure in order not to introduce bacteria or other complications. A noninvasive manner that does not require a technician, cannot introduce bacteria, and that can be performed simply by the subject is much preferred.
It is furthermore desirable to provide a device and method to continuously, or nearly continuously, monitor the levels of the analyte. Intermittent body fluid sampling may not detect transient changes in the analyte while continuous monitoring can.
Examples of desirable analyte measurements for such a device and method include:                blood: glucose        blood: hormones        blood: therapeutic drugs        blood: cocaine        blood: HIV antibodies        interstitial and lymph fluid: cancer precursors        cerebral spinal fluid: Alzheimer precursors        blood: creatinine to monitor kidney function for dialysis        blood: bilirubin, AST, ALD, alkaline phosphatase to monitor liver function in cirrhosis        
Given that diabetes is predicted to become an international epidemic due to changes in the eating habits of the world population and increasingly sedentary lifestyles, noninvasive glucose measurement is of particular interest. Most of the long term affects of diabetes are due to untreated hyperglycemia and currently there is not an effective noninvasive continuous glucose measurement method available. Diabetics are left to painfully sample their blood many times each day in order to determine glucose concentration and adjust their insulin dosage accordingly. The present invention provides a method and apparatus for continuous noninvasive blood glucose monitoring.
Given the critical nature of glucose monitoring, there are a number of known devices in the field for noninvasive optical scanning of a body part followed by data analysis to infer glucose concentration. For example, U.S. Pat. No. 6,675,030 to Ciurczak, et al. discloses a multi-spectral scanner to view a body part and infer the glucose concentration using a mathematical model correlated to the subject using invasive samples.
U.S. Pat. No. 6,236,047 to Malin, et al. discloses a method that illuminates the body part with various optical energies and determines analyte concentration by analyzing the reflected radiation.
U.S. Pat. No. 6,181,957 to Lambert, et al. discloses a method using an optical beam imaged on the eye and determines glucose concentration by analyzing the reflected radiation.
U.S. Pat. No. 6,124,134 to Stark discloses a device that irradiates the body with electromagnetic radiation and determines glucose concentration by analyzing the resulting spectrum.
The basis of the Ciurczak, et al., Malin, Lambert, et al., and Stark inventions is the assumption that the analyte to be measured, or its normal blood compounds, substantially influence the reflected or transmitted portion of electromagnetic radiation.
U.S. Pat. No. 6,681,127 to March discloses a contact lens having a binding site for the analyte and an analyte competitor for the same site. The competitor is fluorescent when in the unbound state.
U.S. Pat. No. 4,344,438 to Schultz discloses a method that includes inserting a capsule having receptors into the blood stream. The concentration of the analyte is determined by the fluorescence of a competitor for the same site.
U.S. Pat. No. 6,197,928 to Tsien, et al. discloses a fluorescent binding protein manufactured within a cell by modifying its DNA sequence to detect analytes.
The basis of the March, Schultz, and Tsien inventions is the provision of a binding site that changes its measurable optical characteristics when bound to the desired analyte.